Field Assisted Sintering and Spark Plasma Texturing of Nd-Fe Magnets with Anisotropic Magnetic Properties

Abstract

Field assisted sintering technologies like spark plasma sintering (FAST/SPS) are attractive alternative methods for the processing of nanocrystalline Nd-Fe-B magnets with well-pronounced anisotropic magnetic properties. This work aims to investigate the potential of hot deformation through FAST/SPS, a method commonly referred to as spark plasma texturing (SPT). SPT with its fine-tuned and closely monitored parameters of heating rate and applied uniaxial pressure has the possibility to yield further refined microstructure and reproducibility when compared to traditional hot deformation. This fine control has the potential to expand beyond the consolidation of nanocrystalline melt-spun starting powder and into other starting materials. Here, the focus is on two different routes of SPT both starting from the same commercial melt-spun Nd-Fe-B powder (Magnequench MQU-F). One deals with the SPT of semi-dense MQU-F compacts (similar to 70% density), while the other focuses on deformation of MQU-F fully dense compacts. Semi-dense compact SPT could lead to new routes for the consolidation of anisotropic Nd-Fe-B magnet scrap without inducing excessive grain growth, while dense compact SPT has more potential for highly textured microstructure. The best balance of properties for a magnet produced from a semi-dense compact was Br = 1.18 T, HcJ = 1203 kA m-1 and (BH)max = 249 kJ m-3, which was achieved by deforming a semi-dense compact at 800 degrees C applying a pressure of 100 MPa. When starting from a dense compact, the best performance was Br = 1.38 T, HcJ = 1180 kA m-1 and (BH)max = 353 kJ m-3. Here, deformation was performed at 750 degrees C under 70 MPa of pressure.